- The colour of a noise describes the shape of its power spectrum: how its sound power is spread over frequencies.
- White, pink, brown (red), blue and violet noise have standard definitions; green and black noise are informal names.
- From brightest to deepest the standard colours run violet (+6 dB per octave), blue (+3), white (0), pink (−3) and brown (−6).
- Black noise has no single definition; most often it means silence.
- Which noise colour is best for sleep has not been tested head to head.
- A 2025 study found no difference in pupil-linked arousal between white, pink and brown noise.
What are the colors of noise?
The colors of noise are names for different shapes of the power spectrum, the way a random sound's power is spread from low to high frequencies. The names come from a loose analogy with light: white light contains all colours equally, so noise with equal power at all frequencies is white, and noise tilted towards the low end is pink or red, the colours at the long-wave end of light.
Some colours have standard definitions. The US telecommunications glossary Federal Standard 1037C defines white, pink, blue and black noise, and brown (red) and violet noise follow from exact power laws. Others, such as green noise, are informal names used by sound apps and recordings, with no agreed formula.
For the standard colours the whole difference is one number: the slope, how many decibels the power changes per octave. Everything else about how they sound follows from it.
Noise colors chart: every colour compared
The chart lists every noise colour from brightest to deepest, with its slope, sound, common use and the research behind it. The dB-per-octave values are exact consequences of the power laws.
| Colour | Power ∝ | Slope per octave | Sounds like | Common use | Research |
|---|---|---|---|---|---|
| Violet (purple) | f² | +6.02 dB | A sharp, thin hiss | Rarely chosen for listening | None on sleep or focus |
| Blue (azure) | f | +3.01 dB | A bright hiss | Rarely chosen for listening | None on sleep or focus |
| White | flat | 0 dB per hertz band (+3 dB per octave) | Radio static | Sleep, masking, babies, focus | Several small sleep studies, baby studies, ADHD meta-analysis |
| Grey | equal-loudness curve | Shaped, not a single slope | Evenly loud to the ear | An even-sounding background | None on sleep or focus |
| Pink | 1/f | −3.01 dB (equal per octave) | Steady rain | Audio reference, sleep, focus | Memory with timed clicks, two sleep studies, ADHD meta-analysis |
| Green | no standard | Peak around 500 Hz | A far waterfall | Sleep, relaxation | None |
| Brown (red) | 1/f² | −6.02 dB | A deep rumble | Sleep, focus | None on its own for sleep or ADHD |
| Black | no standard | Silence, or infrasound | Nothing, or nothing audible | Quiet, earplugs | Earplugs tested in a sleep lab |
A note on white noise's slope: it is flat when you measure power per hertz, and rises by about 3 dB per octave when you measure power per octave, which is closer to how we hear. Pink is the reverse: falling per hertz, flat per octave. Both views are correct; they just use different rulers.
What does dB per octave mean?
Decibels per octave tell you how much the power of a noise changes each time the pitch doubles. An octave is a doubling of frequency: 100 to 200 Hz, 1,000 to 2,000 Hz. A change of 3 dB is a doubling or halving of power, 6 dB a fourfold change, 10 dB tenfold.
So pink noise, at −3 dB per octave, has half the power density in each octave that it had in the one below; because each octave is twice as wide, the total power in every octave comes out equal. Brown noise, at −6 dB per octave, has a quarter of the density each time up, so every octave carries half the power of the one below it. Over ten octaves that is a factor of about a thousand between bottom and top.
Another common unit is dB per decade, a tenfold change in frequency. Pink noise falls by 10 dB per decade and brown by 20 dB per decade. Both descriptions say the same thing.
Brown vs white vs pink noise: how to tell them apart
White noise sounds like static, pink noise like rain, brown noise like a waterfall. That is how the authors of a 2024 meta-analysis of noise and ADHD (Nigg and colleagues) describe them: white noise sounds like static, while pink or brown noise has more power in the lower frequencies and may sound, respectively, like rain or a waterfall.
The quickest way to learn the difference is to switch between them at the same volume. Start the generator with white noise, then turn it down and turn pink up, then brown. Listen to where the sound seems to sit: white noise feels close and in the upper part of the head, brown feels far and low, pink in between.
People also react to them differently. In ratings by more than 1,300 people, white noise felt the most uneasy and brown the most pleasant; the brown noise page describes that study. The body's arousal, however, did not differ, as the next section shows.
| White | Pink | Brown | |
|---|---|---|---|
| Sounds like | Static | Rain | A waterfall |
| Energy | Rising towards the top | Equal per octave | Mostly in the bass |
| Masks best | High sounds | A broad range | Low sounds |
| In depth | White noise page | Pink noise page | Brown noise page |
Do different noise colours affect the body differently?
The few studies that compared noise colours directly found small or no differences in the body. A 2025 study (Erfanian, Chait and Kang, International Journal of Psychophysiology) measured pupil size, a standard marker of arousal, in 31 people while they heard white, pink and brown noise for 10 seconds each. Pupil-linked arousal did not differ between the colours. The exposure was very short, so the result says nothing about an hour or a night.
In a small dental study in children (Kolhe and colleagues, 2024), 40 children aged 8 to 12 were split into four groups of 10: white, pink or brown noise, or cartoon music during a tooth extraction. Anxiety and pain changed in all groups, and pink noise kept the pulse steadiest. With 10 children per group, that is a hint, not a ranking.
In attention research, the 2024 meta-analysis pooled white and pink noise and found no studies of brown. In sleep research, one intensive-care study played white, pink and brown noise on three consecutive days without comparing them. No study has compared the colours head to head for sleep.
What color noise is best for sleep?
No noise colour has been shown to be best for sleep, because the colours have not been tested head to head. Choose the one you find most pleasant at a low volume. The broader evidence, on the white noise page, is that steady noise helps mainly by masking and most clearly in noisy surroundings.
Masking does give a practical rule for choosing. A steady sound hides other sounds most strongly when they share frequencies, so match the colour to what disturbs you:
| What disturbs you | Colour to try first | Why |
|---|---|---|
| Traffic rumble, a lift, bass through the wall | Brown | Most of its energy is in the low range |
| A mix of everyday sounds | Pink | Equal energy in every octave |
| High sounds: a squeaking door, a TV next door | White or pink | More energy in the upper range |
| Middle-range sounds in an otherwise quiet room | Green | Energy concentrated in the middle |
| Your own thoughts in a quiet room | Whichever you find most pleasant, or none | Masking has little to do; the evidence in quiet rooms is weak |
Blue and violet noise are poor choices for sleep: they put almost all their energy in the treble, sound sharp, and leave low sounds uncovered. Whatever colour you pick, keep it quiet; the WHO recommends that continuous noise in a bedroom stay below about 30 dB.
What is black noise?
Black noise has no single definition; most often it simply means silence. Other uses of the term include infrasound, sound below the range of hearing. None of these is a noise you can play for sleep, which is why no generator, ours included, has a black noise button.
If what you want is black noise in the sense of silence, the tools are earplugs and a quieter room, not a sound. The most careful recent sleep-lab study (Basner and colleagues, 2026) compared the two approaches: earplugs prevented nearly all the effects of traffic-type noise on sleep until they started to fail at 65 dBA, while pink noise did not protect sleep and on its own reduced REM sleep. The pink noise page describes the study in detail.
The WHO sets the targets for a quiet bedroom: continuous noise below about 30 dB, single sounds not above 45 dB. If your room meets them, silence may serve you better than any colour.
What are blue noise and violet noise?
Blue and violet noise are the mirror images of pink and brown: their power rises with frequency. Blue noise, also called azure noise, has power proportional to f and gains 3.01 dB per octave. Violet noise, also called purple noise, has power proportional to f² and gains 6.02 dB per octave.
Violet noise is what you get by differentiating white noise, taking the difference between each sample and the one before, just as brown noise is integrated white noise. It also occurs in nature: the thermal noise of water has a violet spectrum.
To the ear both are sharp and thin, with most of their energy in the highest octaves. For sleep or long listening they are an odd choice: they cover low sounds poorly, and a sound with so much treble becomes tiring at any but a low volume. They are worth hearing once, at a low level, to understand the rest of the chart.
What is grey noise?
Grey noise is white noise reshaped so that it sounds equally loud at all frequencies to a listener. It is made by filtering with an equal-loudness curve, for example an inverted A-weighting curve, which boosts the lows and highs where the ear is less sensitive and trims the middle where it is most sensitive.
The idea is the opposite of pink noise. Pink is balanced for the octave structure of hearing; grey is balanced for the loudness sensitivity of hearing. The result sounds flat and even, without the hiss of white or the weight of brown.
Our generator's grey noise is an approximation: pink noise with a boost below about 180 Hz, a smaller boost above about 7,000 Hz and a dip around 3,200 Hz. An exact equal-loudness curve depends on the listening level, so every grey noise is an approximation to some degree.
How the noise colours are made in this generator
Every colour in the generator is computed in your browser from random numbers, nothing is recorded. The mixer plays seven noise colours and seven nature sounds, each with its own volume, offers ready mixes and has a timer from 15 minutes to 8 hours that fades the sound out over the last minute.
| Colour | How it is made |
|---|---|
| White | Independent random samples |
| Pink | White noise through Paul Kellet's refined pink filter (−3 dB per octave) |
| Brown | White noise through a leaky integrator (−6 dB per octave) |
| Blue | Differentiated pink noise (+3 dB per octave) |
| Violet | Differentiated white noise (+6 dB per octave) |
| Grey | Pink noise shaped roughly to the equal-loudness curve |
| Green | Pink noise with a high-pass at 120 Hz, a low-pass at 2,200 Hz and a 7 dB peak at 500 Hz |
Each colour is stored as a seamless loop with a cross-fade at the joint, so there is no click. When you mix colours, each layer starts at a random point, so two layers never line up. Every colour is normalised to the same average level, but they will not sound equally loud, because the ear is more sensitive to the middle than to the extremes; adjust by ear.
Questions people ask
What are the colors of noise?
Names for different shapes of a noise's power spectrum. The standard ones, from brightest to deepest, are violet, blue, white, pink and brown; grey, green and black are further names, the last two informal.
What is the difference between white, pink and brown noise?
White noise has equal power per hertz and sounds like static; pink loses 3 dB per octave and sounds like rain; brown loses 6 dB per octave and sounds like a deep rumble or waterfall.
What color noise is best for sleep?
No study has compared the colours head to head. Choose the one you find most pleasant at a low volume; brown suits low disturbing sounds, white or pink higher ones.
Is brown noise better than white noise?
People rate brown as more pleasant and white as more uneasy, but no study has shown that either is better for sleep. Brown masks low sounds, white masks high sounds.
What is black noise?
An informal term with no single definition; most often it means silence, sometimes infrasound. For sleep, the practical version is earplugs and a quiet room.
What is blue noise?
Noise whose power rises by 3 dB per octave, also called azure noise. It sounds like a bright hiss.
What is violet noise?
Noise whose power rises by 6 dB per octave, also called purple noise. It is differentiated white noise, and the thermal noise of water has a violet spectrum.
What is grey noise?
White noise shaped by an equal-loudness curve so that it sounds equally loud at all frequencies to a listener.
Is green noise a real noise colour?
It has no standard definition; the name is used for pink-like noise with more energy around 500 Hz.
Why are noise colours named after colours?
By a loose analogy with light: white light contains all colours, and noise tilted towards low frequencies is called pink or red after the long-wave end of the spectrum. Brown is the exception: it is named after Brownian motion.
- Wikipedia. Colors of noise (secondary source, based on Federal Standard 1037C), read 30 September 2026.
- Federal Standard 1037C. Telecommunications: Glossary of Telecommunication Terms. United States.
- Erfanian M., Chait M., Kang J. Pupil-linked arousal does not differ between 'white', 'pink' and 'brown' noises. International Journal of Psychophysiology, 2025, 218, 113271.
- Færøvik U. H., Vikene K., Specht K. Put the control back in the control condition: are brown, pink, and white noise neutral control stimuli? Frontiers in Neuroscience, 2025, 19, 1488682.
- Kolhe S., Dialani P., Bondarde P., Pande R., Patil P., Vishwakarma A. P. A comparative evaluation of the effects of white noise, brown noise, and pink noise on dental anxiety of pediatric patients undergoing dental extraction treatment: a randomized control study. Journal of the Indian Society of Pedodontics and Preventive Dentistry, 2024, 42 (4), 273–279.
- Nigg J. T., Bruton A., Kozlowski M. B., Johnstone J. M., Karalunas S. L. Systematic review and meta-analysis: do white noise or pink noise help with task performance in youth with attention-deficit/hyperactivity disorder or with elevated attention problems? Journal of the American Academy of Child and Adolescent Psychiatry, 2024, 63 (8), 778–788.
- Warjri E., Dsilva F., Sanal T. S., Kumar A. Impact of a white noise app on sleep quality among critically ill patients. Nursing in Critical Care, 2022, 27 (6), 815–823.
- Basner M., Smith M. G., Cordoza M., Kayser M. S., et al. Efficacy of pink noise and earplugs for mitigating the effects of intermittent environmental noise exposure on sleep. Sleep, 2026, 49 (5), zsag001.
- Moore B. C. J. An Introduction to the Psychology of Hearing, 6th ed. Brill, 2012.
- World Health Organization. Guidelines for Community Noise, 1999.
The generator computes every colour in the browser from random numbers: pink with Paul Kellet's filter, brown by integrating white noise, blue and violet by differentiating pink and white noise, grey and green by filtering pink noise. On this page it starts with white noise so you can switch to each colour in turn and compare.